Blender scene being ruined for no reason?
You probably need to set up a proper location for the baked cache, within your project folder, preferably with a relative path, so that the fluid data is correctly saved in a safe place, and available next time you open your project file.

It may be getting deleted in the temp folder or unintentionally lost.

Use the path box visible in your screenshot under the Properties Window > Physics > Fluid > Cache path and point it to a safe location, possibly within your current project folder, or next to the blend file. 

After that optionally you may manually move the cache files from the previous temp location if you do not want to rebake, or simply  just bake again to the new folder.